A key vote on the measure is looming.
The Obama administration on Monday endorsed a Senate proposal to rein in the government's most controversial domestic spying program—a move coming just a day before the Senate is slated to start debating the measure.
In a statement from the White House, the administration said it "strongly supports" the USA Freedom Act, a bill from Senate Judiciary Chairman Patrick Leahy that would effectively end the National Security Agency's bulk collection of metadata—the numbers and time stamps of phone calls but not their actual content. The once-secret program was publicly exposed by Edward Snowden last summer.
"This legislation will help strengthen Americans' confidence in the Government's use of these important national security authorities," the Office of Management and Budget said in a statement. "Without passage of this bill, critical authorities that are appropriately reformed in this legislation could expire next summer."
President Obama in January pledged to reform the government's surveillance practices, but said he could only do so when Congress sent him a bill that closely matched his recommended changes.
Leahy's legislation is a rewritten version of a similar bill that passed the House in May with bipartisan support. While the House measure suffered a loss of support from privacy advocates and the tech industry, who said it had been "watered down" during final negotiations, Leahy's bill has earned support from tech companies, privacy and civil-liberties groups, and senior members of the intelligence community.
Among the bill's many provisions, it would require phone companies to retain metadata records, not the government. Intelligence agencies could obtain phone data only after being granted approval from the Foreign Intelligence Surveillance Court. The bill would additionally usher in several privacy and transparency measures, including a more limited definition of what can be considered a surveillance target.
The administration had signaled before that it would support the USA Freedom Act, but the endorsement on Monday was unusually forceful.
It lauded the strengthened "privacy and civil liberties protections" in the Foreign Intelligence Surveillance Act, but noted that the measure preserved "essential authorities that our intelligence and law enforcement professionals need."
"The administration strongly supports Senate passage of ... the USA Freedom Act," the statement read.
The statement did note, however, that the administration was "aware of concerns" from the intelligence community about a provision in the bill to allow an independent privacy advocate to argue before the FISA Court. "The administration anticipates that Congress will address those concerns," it said, possibly referring to amendments that may be offered during Senate debate later this week.
It remains unclear if the bill has enough support to clear the Senate's filibuster-proof threshold of 60 votes. There are likely to be amendments offered on the floor Tuesday from privacy hard-liners, such as Sen. Ron Wyden, and possibly from some defense hawks, including Senate Intelligence Chairwoman Dianne Feinstein.
Feinstein on Monday said she was "not necessarily" a no vote. Her support would be considered a big boost to the bill's prospects, though it is uncertain if enough Republicans will support the measure.
Sarah Mimms contributed to this article.